The synthesis of analogs of tentoxin (cyclo-MeAla-Leu-Me delta Phe-Gly) will be carried out. Each analog will be tested for biological activity and binding to chlorophyll coupling factor-1 (CF1). In addition the conformations of these analogs will be determined in solution by nuclear magnetic resonance spectrometry. Several model cyclic tetrapeptides will be synthesized and analyzed by NMR to facilitate this study. Competitive inhibition experiments between tentoxin and CF1 will be studied. BIBLIOGRAPHIC REFERENCES: Effects of Structure of Active Compounds on Biological Activity and Specificity, D. H. Rich, in Specificity in Plant Diseases, edited by A. Graniti and R. K. S. Wood, 169-184 (1976). A Method for Introducing Secondary Amide Bonds into Strained Cyclic Peptides, D. H. Rich and J. P. Tam, Tetrahedron Letters, 749 (1977).